Today's multi-service switch/router system (also referred to herein as a network element (NE)) often handles communications packets of two or more different services or protocols, such as asynchronous transfer mode (ATM), frame relay (FR), internet protocol (IP), multi-protocol label switching (MPLS), Ethernet, and so forth. For example, IP packets may be routed between two packet-over-SONET (POS) network ports while ATM cells are simultaneously switched between two ATM network ports. The ATM and IP POS network ports may even be sharing the same line interface card and the same thread through the switch fabric thread (or router data backplane). However, multi-service or multi-protocol operation of prior art NEs leads to problems due often to the heterogeneous characteristics of modern services and protocols.
This heterogeneity is illustrated by comparing IP packet to ATM cell traffic. First, IP does not require advance setup of a connection between a source-destination pair. Instead, each packet is independently and non-deterministically routed from its source to its destination, routing decisions being made moment-to-moment by the individual NEs. Thus, the traffic flow within an IP network, or even within the NEs in an IP network is not known in advance, and can significantly shift due to failures in the network, administrative changes, or the like. Further, IP does not reserve network resources, and packets flowing between one source-destination pair compete for resources with packets of other flows. But despite being non-deterministic and non-reserved, IP does have quality of service (QoS) expectations for different types of traffic.
In contrast, ATM requires advance setup of a connection between a source-destination pair and reserves network resources prior to commencing cell traffic between the pair. The connection establishes the deterministic path that all cells will follow between the source-destination pair, and therefore prescribes in advance the routing through the NEs in the traffic path. Thus, unlike IP, the amount of ATM traffic over network paths is known in advance. Accordingly, the network can reserve to a source-destination pair resources sufficient to meet its QoS and bandwidth requirements in view of the current, known network traffic. If insufficient resources are available, the connection request may be refused.
When modern services or protocols with heterogeneous characteristics and QoS expectations, such as non-deterministic IP packets and deterministic ATM cells, flow together in a network, and especially in single NEs, the QoS expectations of traffic carried by one service may often be impaired by traffic being simultaneously carried on other services. This may often be due to conflict for use of shared resources, e.g., buffers, fabric threads, communication links, scheduler service, and the like.
Current NEs generally are not able to adequately respond to such problems, principally because current switch fabric and router backplanes are designed for only one service or protocol. Often cell-based, ATM-like switching fabrics are used in IP routers to route and forward IP-only traffic within an NE from an input network port slot to an output network port. Similarly, the so-called multi-service NEs are also designed with ATM in mind so that data must be forwarded through the switch in ATM-like cells. This requires that incoming communication packets of other services or protocols, such as IP, be segmented as best as possible for transport through the switch in ATM cells and that the QoS classes of these other services be mapped as best as possible to ATM QoS classes. Further precautions may be needed to prevent ATM QoS goals from being compromised by competition from other services.
Without an adequate response to such problems, network operators often must pick one service as more important than the others (e.g., ATM more important than IP), regardless of the reality of changing user needs.